The goal of this project is to develop and test a peri-operative confocal imaging-guided approach for laser ablation of basal cell carcinomas (BCCs). BCCs are among the most common malignancies in the world, with an estimated 2.5 million new cases diagnosed every year in the USA and 700,000 in Europe and Australia. Mohs surgery, guided by frozen pathology, is the standard treatment. However, the procedure is labor- intensive and expensive, with treatment costs of about $2 billion every year in the USA. Consequently, less invasive and less expensive non-surgical alternative therapies are being increasingly adopted. Laser ablation is particularly effective for minimally invasive removal of superficial and early nodular types of BCCs (about 600,000 cases per year in the USA and 200,000 in Europe and Australia). Skin can be ablated in m-thin layers in a controlled manner. However, tissue is vaporized such that there is none available for immediate pathological evaluation for the presence or clearance of tumor. (One may say that there's plenty of tissue remaining on the patient that can be taken for pathology, but this would defeat the very purpose of a less invasive approach.) The lack of pathological feedback results in variable efficacy and limited cure rate. A high-resolution nuclear-level optical imaging approach such confocal microscopy may detect the presence or clearance of residual BCCs directly on the patient, and provide immediate pathology-like feedback. However, ablation produces thermal coagulation and loss of viability in the remaining underlying tissue (wound), which may subsequently impede the uptake of a contrast agent for labeling nuclear morphology and imaging of residual tumor. Our hypothesis is that adequate tissue viability may be preserved by controlling the thermal coagulation with optimal choice of ablation parameters (pulse duration, fluence, number of pulses, wave- length). This may subsequently allow uptake of contrast agent and detection of residual BCC tumor in vivo. Such an imaging-guided approach may improve the efficacy and cure rate of ablation for superficial and early nodular BCCs. About 800,000 patients (worldwide) may benefit, per year, with a less invasive procedure. Preliminary studies on excised human skin specimens confirms our hypothesis. Testing on five BCCs in vivo demonstrates the potential for peri-operative imaging directly on patients to guide ablation. The specific aims are to (1) investigate depth of thermal coagulation and viability of tissue in the underlying wound versus two ablation parameters (fluence, number of pulses), and determine optimal parameters for preserving adequate viability; (2) determine the uptake of contrast agent (acetic acid) versus optimal ablation parameters in excised human skin specimens, with quantitative validation against pathology; (3) simulate implementation on patients in vivo, by testing feasibility for detecting clearance of BCCs on excised human skin specimens versus optimal ablation parameters, with quantitative validation against pathology; (4) test feasibility of peri-operative imaging- guided ablation on patients, with quantitative validation against pathology and clinical follow-up.